Better error message, when pyserial is missing. (#2299)

Author: janiversen

pymodbus/client/serial.py

@@ -1,10 +1,11 @@
 """Modbus client async serial communication."""
 from __future__ import annotations
 
+import contextlib
+import sys
 import time
 from collections.abc import Callable
 from functools import partial
-from typing import TYPE_CHECKING
 
 from pymodbus.client.base import ModbusBaseClient, ModbusBaseSyncClient
 from pymodbus.exceptions import ConnectionException
@@ -14,15 +15,9 @@
 from pymodbus.utilities import ModbusTransactionState
 
 
-try:
+with contextlib.suppress(ImportError):
     import serial
 
-    PYSERIAL_MISSING = False
-except ImportError:
-    PYSERIAL_MISSING = True
-    if TYPE_CHECKING:  # always False at runtime
-        # type checkers do not understand the Raise RuntimeError in __init__()
-        import serial
 
 class AsyncModbusSerialClient(ModbusBaseClient):
     """**AsyncModbusSerialClient**.
@@ -82,7 +77,7 @@ def __init__(  # pylint: disable=too-many-arguments
         on_connect_callback: Callable[[bool], None] | None = None,
     ) -> None:
         """Initialize Asyncio Modbus Serial Client."""
-        if PYSERIAL_MISSING:
+        if "serial" not in sys.modules:
             raise RuntimeError(
                 "Serial client requires pyserial "
                 'Please install with "pip install pyserial" and try again.'
@@ -191,6 +186,11 @@ def __init__(  # pylint: disable=too-many-arguments
             framer,
             retries,
         )
+        if "serial" not in sys.modules:
+            raise RuntimeError(
+                "Serial client requires pyserial "
+                'Please install with "pip install pyserial" and try again.'
+            )
         self.socket: serial.Serial | None = None
         self.last_frame_end = None
         self._t0 = float(1 + bytesize + stopbits) / baudrate

pymodbus/transport/serialtransport.py

@@ -4,6 +4,7 @@
 import asyncio
 import contextlib
 import os
+import sys
 
 
 with contextlib.suppress(ImportError):
@@ -18,6 +19,11 @@ class SerialTransport(asyncio.Transport):
     def __init__(self, loop, protocol, url, baudrate, bytesize, parity, stopbits, timeout) -> None:
         """Initialize."""
         super().__init__()
+        if "serial" not in sys.modules:
+            raise RuntimeError(
+                "Serial client requires pyserial "
+                'Please install with "pip install pyserial" and try again.'
+            )
         self.async_loop = loop
         self.intern_protocol: asyncio.BaseProtocol = protocol
         self.sync_serial = serial.serial_for_url(url, exclusive=True,

test/sub_client/test_client.py

@@ -245,16 +245,6 @@ async def test_client_instanciate(
     with pytest.raises(ConnectionException):
         client.execute(ModbusRequest(0, 0, 0, False))
 
-async def test_serial_not_installed():
-    """Try to instantiate clients."""
-    with mock.patch(
-        "pymodbus.client.serial.PYSERIAL_MISSING"
-    ) as _pyserial_missing:
-        _pyserial_missing = True
-        with pytest.raises(RuntimeError):
-            lib_client.AsyncModbusSerialClient("/dev/tty")
-
-
 async def test_client_modbusbaseclient():
     """Test modbus base client class."""
     client = ModbusBaseClient(